Modified Angstrom coefficients for the sunshine-irradiation correlation

Abstract

Model parameters are achieved very often by the least square method (LSM) and regression technique between irradiation and bright sunshine data. A new variance method (VRM) is used for finding the modified Angstrom coefficients (<i>a, b</i>)<i> </i>using the same set of data. Some other methods (such as latitude method (LM), Reitveld method (RVM) etc.), which

are dependent on geographical as well as meteorological parameters, are also employed in this work. The study of levels of performance or these methods shows that the VRM and LSM predict the global solar radiation <i>H </i>with better accuracy than other methods. The index of agreement <i>d </i>indicates a little better performance of VRM over LSM. Latitude method (LM) does not give satisfactory results at lower latitude ϕ of the site. Analysis shows that the LM might be applicable for the latitudes ≥10°N safely with a maximum deviation of 6 % where only the sunshine data are available. Polynomial behaviour or the sun shine- irradiation relationship along with the linear form is also studied to know actually which form belongs to them.